In conventional injectors for injecting fuel, a control valve is moved by activating an actuator, for example, a magnetic or piezoelectric actuator. The control valve is in hydraulic communication with a nozzle needle, the nozzle needle opening or closing the injector as a function of the state of the control valve.
In addition, an activation starting time and activation ending time of the activation of the actuator may be ascertained. The determination of a closing time of the control valve is described in German Patent Nos. DE 3 609 599 A1 or DE 3 843 138 A1.